Bill Davidsen wrote:
This question came out of a discussion of nesting (or stringing if you
like) disk images using qcow.
If I have an unpatched install image, say CentOS-5.2 (box "A" below).
and I make a copy of that with qcow and apply patches to that copy
(box "B" below), everything is just fine. But if I should make a
working qcow image from the patched version (box "C" below), which
works fine initially, what would happen if I applied patches to the
"current" version? I assume that would mess up the application
version, since it's a physical copy, but I'd like to be sure.
______________
| [A] |
| orig release |
|______________|
||
{qcow copy|
||
____________________
| [B] |
| patched to current |
|____________________|
||
{qcow copy}
||
_________________________
| [C] |
| fully config. app. svr. |
|_________________________|
I could play with union filesystem, network mounting of /var and /usr,
and other tricks, but I thought I'd check that this really is a
problem, and the current version needs a "real" copy to the app
server, and then the app server needs to be patched after that.
Changing anything except the last image in the chain is liable to
break. In other words: once you use an image as a base for another
image, this first image must never change.
--
Do not meddle in the internals of kernels, for they are subtle and quick to
panic.
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